PROJECT SUMMARY Medicaid, the largest health insurance sector in the U.S., with the most vulnerable individuals, is the least- well understood. There is little research on the effects of the structure of state Medicaid programs on access, patterns of care and outcomes of substance use disorder (SUD) care. States provide Medicaid benefits either through publicly managed Fee-for-Service (FFS) systems or by contracting with private Medicaid Managed Care (MMC) plans. Despite widespread adoption of MMC, its role is not well-understood, especially its effects on SUD treatment and service disparities. Little is known about any differences in SUD treatment between traditional FFS Medicaid and private MMC plans or differences across different types of managed care plans with different approaches to SUD treatment. The proposed study makes use of innovative random assignment methods to address this challenge in the Medicaid sector. In the proposed project, we apply a select group of metrics for assessing access, patterns of care and outcomes of SUD treatment, to describe the performance of systems, health plans, and provider groups in New York. We then conduct stratified analysis by race/ethnicity, gender, and rurality to identify which programs and plans have better outcomes and identify if there are service disparities. Our project uses qualitative methods to help interpret our results through in-depth interviews, and to provide insight on the interpretation of findings and suggest practice and policy changes.